Two-speed driving mechanism



Oct' 9, 1945. J. A. LAwLr-:R ETAL Two-SPEED DRIVING MECHANISM Filed Feb. 7, 1944 @www Oct 9, 1945 J. A. LAwLER ETAL TWO-SPEED DRIVING MECHANISM Filed Feb. 7, 1944 2 Sheets-Sheet n 1111 Il Enum-E Patented st. 9, 1945l l l l n TWO-SPEED DRIVING MlECz Y .lohn A. Lawler, Los Angeles, Calif., and Samuel K. Hoiman, Williamsport, Pa., assignors to The Aviation Corporation, New York, N. Y., a corporation of Delaware Application February 7, 1944, Serial No. 521,358

1'? Claims. (Cl. Z4- 290) The invention relates to two-speed driving splined at 2i between the cage sides I5 and i'l to mechanism. a hollow shaft 22 and meshes with the planet One object of the invention is to provide congears i3; a ring 23 which is provided with internal trol means for two-speed driving mechanism gear teeth2t which mash with planet gears I3 which is adapted to gradually effect the speed 5 and with external gear teeth 25 which constitute changes to avoid severe shock to gearing when the output gear; and a ring-carrier which comspeed-changes are made. prises sides 2S and 2l between which the ring is Another object of the invention is to provide a fixed. Carrier side 26 is journaled in a bushing 28 two-speed driving mechanism which is controlled which is xed in a wall of the casing a and carrier by gripping devices of the friction plate type and 1o side 2l is journaled on the input shaft Il. The in which provision is made for a relatively low sun-gear shaft 22 extends through the input shaft initial engaging-pressure for permitting slippage il and is provided With bushings 29 which are to effect a, gradual initial gripping of the plates journaled in the input shaft. The shaft i9 ex and a subsequent greater pressure for positive tends through, and is journaled in bushings in, the engagement, sun-gear shaft 22 and is also journaled in a bush- Another object of the invention is to provide iming 3i in the hub of carrier side 26. This transproved two-speed driving mechanism of the type mission. when the sun-gear and its shaft -22 in which the speed changes are controlled by are rotated with the input shaft il and the cage alternate engagement of a pair of friction plate OI the planet geaI's l3.Wi11 drive the Output Shaft gripping devices which are controlled by -hy- 20 25 at low speed, or at the same speed as the input draulically shifted elements for pressing the de- Shaft. When the sun-gear is locked against IOtaviees into gripping relation, tion, the cage on the input shaft Il will impart Another object of the invention is to provide Planetary movement to gears i3 and Cause the driving mechanism of this type in which the gear ring 23 and output geal- 25 t0 be driven at` a clutch-plates are pressed together with an initial 25 higher ratio than theuput shaft il. fOr high low face-pressure and a subsequent higher hyspeed operation.

draulic pressure to effect positive engagement of v The mechanism fOr Varying the speed ratio of the plates, so that a relatively low number of the Output gear 25 relatively t0 the input gear 9 plates will provide the required gripping. comprises a drum b which is xed to and rotatable other objects'of the invention will appear from 30 with the shaft 22 and the sun-gear 20 thereon; a the detaned description brake, generally designated c, for locking the drum The invention consists in the several novel feab. the Sull-gea!` 20 and its Shaft 2| against rotatures which are hereinafter set forth and more tiOILfOr high Speed Operation 0f the transmission; particularly defined by claims at the conclusion and a disk Clutch d between the drum b t0 Which hereof. the sun-gear shaft is xed, and the shaft I9 which In the drawings: is rotatable by the cage-side Il, for-rotating the Fig. 1 is a longitudinal section of a two-speed sun-gear 2U with the planet gear cage which is driving mechanism embodying the invention, the adapted to bodily rotate the planet gears I3 for parts being shown in high-speed driving. the low speed operation of the transmission.

Fig. 2 is a section taken on line 2-2 of Fig. 1. 40 The drum b'encloses the brake c and the clutch Figg is a longitudinal section illustrating one cl and comprises a head or flange 33 which is of the engaging devices of the driving mechanism integral with the shaft z2, an annum or cylinin its neutral position. drical member 34 which isbolted to head 33 and The inventori` is exemplified 'in a two-Speed a head a5 which is bolted to member at and protransmission which is mounted in and enclosed vided with a hub 35 which is journaled in a by a stationary casing a.' This transmission combushing 31 n one* of the Walls of the casing a prises an input gear 9 which is integral with a hollow input shaft i l which is journaled in a The brake c comprises a series of plates or disks 39 which are slidably splined at 40 to the annular bushing l2 ma wall of the ,casing a; a set of lanet gears I3 which are journaled on stud shatots ld, 50 member 34 of the drum b' allemal@ dlslls or plates respectively; a rotatable cage for the planet gears @l and a' hollow shaft Seclllon 42 -Wlllcllextends and their shafts which includes a side member I5A through the hub 36 of drum'head 34 and ls xedly which is splmed at l5 to the input shaft H, and keyed at 43 to a ring or plate it which is secured an opposteside member l1 which is Splined as at by bolts 45 to the casing a for securing shaft 40 I8 to a hollow shaft I9; a sun-gear 20 which is 55 against rotation. The intermediate disks 4I are slidably splined at 48 to the stationary shaft section 40.

The clutch d comprises a series of plates or disks 48 which are slldably splined at 49 to the annular member 34 of the drum b, and alternate section 42 and the drum will hold the shaft 22 and the sun-gear 20 against rotation. At this time the disks of the clutch d will be disengaged so that the cage-side l1 and shaft I8 will be free to be rotated by the stud-shafts i4 and cage-side I5 from the input shaft Il. When the disks of brake c are disengaged and the disks of clutch d are engaged, the drum b will be free to be rotated around shaft section 42 and will be driven to drive the sun-gear 20 and its shaft' 22 with the input shaft Il from the cage-side i1 through shaft i9, and the engaged disks 48, 48 which are splined respectively to the drum and to shaft I9.

The brake c and the clutch d are hydraulically controlled for alternate gripping engagement, so that when one of them is engaged the other will be free. A transverse partition wall 58 is integrally formed with the annular member 88 ofthe drum at its longitudinal center between the clutch d and the brake c and cylinders 55 and 58 are formed in the drum at the opposite sides of said wall, respectively. A main piston 51 is slidably fitted in the cylinder 55 and a main piston 58 is slidably tted inthe cylinder 58. Pistons 51 and 58 are secured respectively on the ends of a hollow shaft 58 which extends through and is slidable in a hub 88 which is integrally formed with the Wall 54. Said main pistons are secured against annular shoulders 8| on the opposite ends of shaft 59 by iianged collars 62 which are screw-threaded into the shaft so that, both of said pistons will move with said shaft and relative movement between the pistons will beV prevented. Piston 51 is rotated with the drum by the inner plate 84 of the brake c. Plate 64 is slidably splined at 55 to piston 51 and to the annular member 34 of the drum. Piston 58 is rotated with the drum by the inner clutch plate 68 of the clutch d. Plate 88 ls slidably splined as at 81 to the hub of said piston and to the annular member 34 of the drum. The endwise movement in opposite directions of the pistons 51, 58 is limited by the ends of the hub 88 on the wall 54.

Fluid under pressure, usually oil, and under selective control, for shifting the piston 51 and the disks of the brake c into gripping relation and locking the drum b against rotation, is delivered into the cylinder 55 through a duct 89 and an annular peripheral channel 1D in the fixed shaft-section 42, and a duct 1I whichis formed in the head 35 and member 34 of the drum and communicatively connects the annular channel 10 and the inner end of cylinder 55. Fluid under pressure is delivered into the cylinder 5B for shifting the piston 58 and the disks of the clutch d into gripping relation, through a duct 13 and an annular channel 14 in fixed shaftsection 42 and a duct 14 which is formed in the head 35 and member 34 of the drum and communicatively connects channel 14 and the inner end of cylinder 5B. The fluid is exhausted from the cylinders through the conduits.

A series of three combined spring and iiuid pressure operable devices, generally designated e, is mounted in each oi' the main pistons 81 and 58 for engaging the disks of the brake c and the clutch d, respectively. when said pistons are hydraulically shifted. The engaging devices carried by each of the main pistons are alike in number. construction and operation, so that Ya description of one is applicable to all of them.

Each engaging device comprises a cup-shaped piston member or auxiliary piston which is pro--` vided with an outer end wall 18 for frictionally engaging the inner plate of the brake c or of the clutch d and a cylindrical skirt 11 which is slidably fitted in an auxiliary cylinder 18 which is formed in a main piston and provided with an inner end wall 19. Outward movement of member e in cylinder 18 is limited by a bolt which is provided with a head 8| adapted to abut against the end wall 18 of cylinder 18 and a nut 82 fitting in a recess in the end wall 18 of the auxiliary piston. A coil spring 84 between tlie outer end wall 18 of the auxiliary piston and the inner wall 18 of cylinder 18 is adapted to force said piston outwardly within the limit permitted by the bolt 88 when hydraulic pressure is not applied internally to said piston. Angular orifices 85 extend through the end wall 19 oi' auxiliary cylinder 18 for the iiow ofv iluid into said cylinder 1B from one of the main cylinders 55 and 88 in the drum. An annular valve 88 around bolt 80 is 'pressed against the inner face oi' the end wall 19 of cylinder V"I8 by a spring 81 for restricting the flow of iiuidfrom Aone of the main cylinders in the drum through orifices 85 into the auxiliary cylinder 18. The skirt 11 of the auxiliary piston is provided with one or more exhaust ports 88 which permit fluid to ow out of the auxiliary cylinder 18 when the auxiliary piston is in its normal extended position. Ports 88 are adapted to be closed by the slide valve action of the skirt 11 during the initial inward movement of the auxiliary piston in its cylinder 18.

When fluid under pressure is delivered to one of the main cylinders 55, 56, the main piston therein will be shifted outwardly by the hydraulic iiuid. The pressure multiplied by the area of each main piston is greater than the pressure multiplied by the pressure-exposed area of the auxiliary piston carried by each main piston plus the total force exerted by the springs 84 against said auxiliary pistons, and therefore each main piston will be shifted by fluid under pressure in the main cylinder in which it is slidable until the outer main piston is arrested by the hub 88 of the wall 54. During each outstroke of the main plston produced by the admission of fluid under pressure to the main cylinder in which it is slidable, said main piston will initially move the auxiliary piston carried thereby to exert pressure against one of the inner disks through springs 84 in the auxiliary cylinder 18 so that the initial pressure against said plate will be limited correspondinglyto the force of said springs. As soon as the auxiliary pistons engage their associated clutch plates, the auxiliary cylinders 18 vwill close the ports 88 in the skirts 11 of the auxiliary pistons, and the orices 85 and valve 88 will restrict the inflow bf fluid from one of the main cylinders into the auxiliary cylinders in the main piston suiliciently to delay the erlectiveness of hydraulic pressure in the auxiliary cylinders 18 on the auxiliary pistons. surfaces of end-wall 18 will be pressed outward- Initially, the engaging' ly solely by springs 84 which will permit a degree of initial slippage in the brake c or the clutch d for gradually starting-the gearing or gradually changing its speed. After the initial engagement of the end-walls 1.8 of the auxiliary pistons with the inner plate of the set of plates to be engaged, the ports 88 in the skirt 11 of the auxiliary pistons will have slid into and have been closed by the surrounding walls of the auxiliary cylinders 18. The fluid from the main cyl inder will be forced through the orifices 85 past the valves 86 into the auxiliary cylinders 18 until the fluid eventually fills the latter cylinders and the pressure therein becomes substantially equal to the hydraulic pressure in the main cylinder. The force of the springs 80 and the hydraulic pressure in the auxiliary cylinders 18 of the main piston will then be cumulated against the end- Wall 16 of the auxiliary pistons and thus force the associated set of plates into positive gripping relation. The rate of flow of the fluid into the auxiliary cylinders 18 is controlled by the area of orifices 85 and the amount of flow restriction by the spring-pressed valve 86. The timing in the change from spring pressure to combined spring and hydraulic pressure can be varied as desired to effect the desiredgradual starting or speed changes by variation of the area of'the orifices 85 and the springs 86. When fluid is exhausted from a main cylinder, the main piston therein will be shifted to its neutral position by the springs 88 in the auxiliary cylinders in said piston, as illustrated in Fig. 3. The fluid in the auxiliary cylinders 18 will then exhaust through the ports 88 in the skirts 11 of the auxiliary pistons at the outer side of the main pistons so that during the initiation of the next engaging Operation no fluid under pressure will be present in the auxiliary cylinders.

When fluid is admitted to the main cylinder 55, the auxiliary pistons carried by the main piston 51'will engage the disks of the brakevc, initially by. spring pressure and then by combined spring and hydraulic pressure, as before described. The drum b will then be locked against rotation so that the sun-gear 20 will be locked against rotation for the high speed operation of the transmission. When fluid under pressure is admitted to the main cylinder' 56, the piston 58 will be shifted to cause theplates of -the clutch d to be initially engaged by spring and then by combined spring and hydraulic pressure applied to the auxiliary pistons in piston 58, as before described. The drum b will then be rotated from the cageside I1 through shaft i8 and the clutch d to cause the sun-gear Z and its shaft 22 to rotate with the input shaft l i for low speed operation of the transmission. s

In these operations of the transmission, the initial force for engaging a set of plates into gripping relation is derived from the springs 84 so with a drum having two pressure chambers or cylinders on opposite sides of the wall 54 and main pistons which are connected to move together, as'by shaft 59, are that: under variations in the centrifugal force resultingfrom the variations in the speed of rotation of the cylinders, the centrifugal force of oil in both cylinders will be oppositely exerted on the pistons and neutralized; the auxiliary cylinders 18 are located adjacent the outer peripheryof the piston so that the oil therein, during clutch engagement of the auxiliary pistons, will also be subjected to great centrifugal force to increase the pressure of endwalls 18 against the engaged clutch or brake; and the balancing effect of the oil columns in the head 35 and in the main cylinders will exert substantially an equal and opposite pressure per unit area in the opposite direction to prevent outflow of the oil through conduits 1| and 14.

This application is a continuation in part of' an application filed by us May 26, 1943, Serial No. 488,488.

The invention exemplifies two-speed clutch and brake controlled gearing which provides for gradually bringing the driving and driven elements to equal speed and for gradually securing some of them against rotation, which is of importance in the operation of enginedriven.devices such as superchargers and for positive driving at both speeds, with a minimum number of clutch-plates. The invention also exemplifies improved twospeed driving mechanism in which the speed is controlled by hydraulic means arranged between a pair of coaxially arrangedplate-clutches. a

The invention is not to be understood as restricted to the details set forth, since these may be modified Within the scope of the appended -claims without departing from the spirit and scope of the invention.

Having thus described the invention, what we claim as new and desire to secure by Letters Patentis:

1. Mechanism for shifting frictionalgripping elements of a transmission into gripping relation comprising, a hydraulically shiftable member, a piston movably supported in said member proinded with means for forcing the elements into gripping relation, spring-means between said member and said piston for applying initial engaging-pressure to the elements, and means in and carried by said member for successively applying hydraulic engaging-pressure to the piston cumuiatively with the spring means.

' 2. Mechanism for shifting frictional gripping elements of a transmission into gripping relation comprising a hydraulically shiftable member, a piston movably supported in said member, provided with means for forcing the elements into that slippage can occur until the output gear is I brought toward its full speed in a change from neutral to low or high speed, or from low to high or high to low, and as the hydraulic pressure in the auxiliary cylinders becomes effective, the plates of each set will be substantially synchronized and pressed together with the necessary force for positive driving. This construction makes it -possible to provide for a given load with the minimum number of clutch plates, and the duration of the slip period is dependent upon the rate of flow under pressure into the auxiliary cylinders carried by the main piston.

The advantage of the construction described gripping relation, spring-means between said member and said piston for applying initial engaging-pressure to the elements, means in and carried by said member for successively applying hydraulic pressure to the piston cumuiatively with the spring means, and restricted flow valvemeans for controlling the flow of fluid to the piston.

3. Mechanism for shifting frictional gripping elements of a transmission into gripping relation comprising, a hydraulically shiftable member, a piston movably supported in said member provided with -means for forcing the elements into gripping relation for the piston in said member, spring-means between said member and said piston for applying initial engaging-pressure to the elements, and means in and carried by said member for conducting fluid under pressure into the cylinder and successively applying hydraulic engaging-pressure to the piston cumulatively with the spring-means.

4. Mechanism for shifting frictional gripping elements oi! a transmission into gripping relation comprising, a hydraulically shiftable member, a piston movably supported in said member provided With a surface for forcing the elements into gripping relation, a cylinder for the piston in said member, spring-means between said member and said piston for applying initial engaging-pressure to the elements, means in and carried by said member for conducting fluid under pressure through the member to the cylinder and piston, and means for controlling the iiuid to the cylinder for cumulating its pressure with the springmeans. V f

5. Mechanism for engaging frictional gripping elements of a transmission comprising a main cylinder, a hydraulically operable main piston in the main cylinder, an auxiliary cylinder in the main piston, an auxiliary piston slidably mounted in the auxiliary cylinder, spring-means between the main piston and the auxiliary piston for applying initial engaging-pressure to the elements, and means for controlling the flow of fluid into the auxiliary cylinder from the main cylinder for successively applying hydraulic pressure to the auxiliary piston cumulatively with the spring pressure.

6. Mechanism for engaging frictional gripping elements of a transmission comprising a main cylinder, a hydraulically operable main piston in the main cylinder, an auxiliary cylinder in the main piston, an auxiliary piston slidably mounted in the auxiliary cylinder, spring means between the main piston and the auxiliary piston for applying initial engaging-pressure to the elements, and valve means in the auxiliary cylinder for controlling the flow of fluid into the auxiliary cylinder from the main cylinder for successively applying 'hydraulic pressure to the auxiliary piston cumulatively with the spring pressure.

7. Mechanism for engaging frlctional gripping elements of a transmission comprising a main cylinder, a hydraulically operable main `piston in the main cylinder, an auxiliary cylinder in the main piston, an auxiliary piston slidably mounted in the auxiliary cylinder, spring-means between the main piston and the auxiliary piston for applying initial engaging-pressure to the elements, valve means in the auxiliary cylinder for controlling the ow of fluid into the auxiliary cylinder from the main cylinder for successively applying hydraulic pressure to the auxiliary piston cumulatively with the spring pressure, and an exhaust duct for the iluid in the auxiliary cylinder, open when the auxiliary piston is in its normal position, and closed by the movement of the auxiliary piston for returning iiuid in the auxiliary cylinder for cumulating the hydraulic and spring pressures.

8. Mechanism for engaging frictional gripping elements of a transmission comprising a main cylinder, a hydraulically operable main pistonI in the main cylinder, an auxiliary cylinder in the main piston adjacent the periphery of the main cylinder, an auxiliary piston slidably mounted in the auxiliary cylinder, spring-means between the main piston and the auxiliary piston for applying initial engaging pressure to the elements, and means orcontrolling the ilow of fluid into the auxiliary cylinder from the main cylinder for successively applying hydraulic pressure to the auxiliary piston cumulatively with the spring pressure.

9. Mechanism for shifting frictional gripping elements of a transmission into a gripping relation comprising a hydraulically operable main cylinder, a main piston in the main cylinder, means for conducting hydraulic fluid into the main cylinder for the operation of the main piston, a series of auxiliary ,cylinders in the main piston, auxiliary pistons in the auxiliary cylinders, respectively, and provided with means for forcing the elements into gripping relation, spring-means in the auxiliary cyllndersfor initially and yieldingly Pressing the auxiliary pistons into position to force the Velements into gripping relation, and means for conducting nuid from the main cylinder into all of the auxiliary cylinders, for successively applying hydraulic engaging pressure to the piston cumulatively with the spring-means.

l0. Mechanism for shifting frictional grip.. ping elements of a transmission into a gripping relation comprising a hydraulically operable main cylinder, a. main piston in the main cylinder for the operation of the main piston, a series of auxiliary cylinders in the main piston, auxiliary pistons in the auxiliary cylinders, respectively, and provided with means for forcing the elements into gripping relation, spring-means` in the auxiliary cylinders for initially and yieldingly pressing the auxiliary pistons into position toi force the elements intol gripping relation, means for conducting fluid from the main cylinder into all of the auxiliary cylinders, and means .for controlling the liow into the auxiliary cylinders for successively applying hydraulic engaging pressure to the piston cumulatively with the spring means.

11. Mechanism for shifting frictional gripping elements of a transmission into a gripping relation comprising a hydraulically operable main cylinder, a main piston in the main cylinder, means for conducting hydraulic fluid into the main cylinder for the operation of the main piston, an 'annularly arranged series of auxiliary cylinders in the main piston, auxiliary pistons in the auxiliary cylinders, respectively, and provided with means for forcing the elements into gripping relation, means for conducting uid from the main cylinder into all of the auxiliary cylinders, the pressure exposed area of each main piston being greater than the total exposed.

area of the auxiliary pistons, and means for restricting the flow into the auxiliary cylinders for applying hydraulic engaging pressure to the piston.

12. Mechanism for shifting frictional gripping elements of a transmission into a gripping relation comprising a hydraulically operable main cylinder, a main piston in the main cylinder, means for conducting hydraulic fluid into the main cylinder for the operation of the main piston, a series of auxiliary cylinders in the main piston, cup-shaped auxiliary pistons in the auxiliary cylinders, respectively, provided 'with closed ends for forcing the elements into gripping relation, spring-means in the auxiliary cylinders for initially and yieldingly pressing the auxiliary pistons into position to force the elements into gripping relation, means for conducting fluid from the main cylinder into all of the auxiliary cylinders, and means for controlling the ow into the auxiliary cylinders for successfully applying hydraulic engaging pressure to the piston cumulatively with the spring-means.

13. Mechanism for shifting frictional gripping elements of a transmission into gripping relation, comprising a main cylinder, a hydraulically operable main piston in the main cylinder, an auxiliary cylinder in the main piston, an auxiliary.piston slidably'mounted in the auxiliary cylinder provided with a closed end for pressing the elements together and a skirt slidable in the auxiliary cylinder, a spring between said end and the opposite end of the auxiliary cylinder, a bolt carried by .the auxiliary piston for limiting the outward movement of the auxiliary piston in the auxiliary cylinder, a spring between the auxiliary piston and the auxiliary cylinder for normally shifting the piston outwardly with in the limits of the stop bolt, and means in the auxiliary cylinder for admitting uid under pressure to the auxiliary cylinder,

14. Mechanism for shifting frictional gripping elements of a transmission into gripping relation, comprising a main cylinder, a hydraulically operable main piston in the main cylinder, an auxiliary cylinder in the main piston, an auxiliary piston slidably mounted in the auxiliary cylinder provided with a closed end for pressing the elements together and a skirt slidable in the auxiliary cylinder, a spring between said end and the opposite end of the auxiliary cylinder, a bolt carriad by the auxiliary piston for limiting the outward movement of the auxiliary piston in the auxiliary cylinder, a spring between the auxiliary piston and the auxiliary cylinder for normally shifting the piston outwardly within the limits of the stop bolt, a duct in the auxiliary cylinder for admitting uid under pressure to Y the auxiliary cylinder, and a. spring-pressed valv around the bolt for closing said duct.

15. Mechanism for shifting frictional gripping elements of a transmission into gripping relation, comprising a main cylinder, a hydraulically operable main piston in the main cylinderfan auxiliary cylinder in the main piston, a cupshaped auxiliary piston slidably mounted in the auxiliary cylinder provided with a closed end for pressing the elements together and a skirt slidable in the auxiliary cylinder, a spring between said end and the opposite end of the auxiliary cylinder, a bolt carried by the auxiliary piston for limiting the outward movement of the auxiliary piston in the auxiliary cylinder. a spring within the skirt between the auxiliary piston and the the pistons, auxiliary auxiliary cylinder for normally shifting the plston outwardly within the limits of the stop bolt, a duct in the auxiliary cylinder for admitting iluid under pressure to the auxiliary cylinder, a springpressed valve for closing said ports, the skirt of the auxiliary piston being provided with an exhau`st port normally open at one side of the main piston.

16.-The combination with a two-speed transmission which comprises planetary gearing, a drum secured to the sun-gear, a plate-type clutch at one end of the drum for driving the drum from the sun gear, and a plate-type brake in the other `end of the drum for locking the drum against rotation, of a central cross-wall in the drum, main cylinders in the drum at opposite sides of the cross-wall, respectively. main pistons slidable in said cylinders, respectively, a shaftextending Vthrough the cross-wall and connecting the main pistons for conjoint endwise movement, means for conducting fluid under pressure into the main cylinders, auxiliary cylinders in each of pistons in the auxiliary cylinders, and lmeans for conducting fluid under pressure from the main cylinders into the auxiliary cylinders for forcing the auxiliary pistons in each main piston, respectively, into pressure-engagement.

17. The combination with two-speed transmission gearing which comprises planetary gearing,

a drum secured to thesun-gear, a plate type clutch at one end of the drum for driving they drum from the sun gear, and a plate type brake in Ithe other end of the drum for locking the drum against rotation, of a central cross-wall in the drum, main cylinders in the drum at opposite sides of the cross-wall, respectively, main pistons slidable in said cylinders, respectively, a shaft extending through the cross-wall and connecting the main pistons for conjoint endwise movement, means for conducting uid under pressure into the main cylinders, auxiliary cylinders in each of the pistons, auxiliary pistons in the auxiliary cylinders, spring-means between the main pisj tons and the auxiliary pistons, and means for conducting fluid under pressure from the main cylinders into the auxiliary cylinders for cumulatively forcing the auxiliary pistons in each main piston, respectively, into pressure-engagement.

- JOHN A. LAWLER.

SAMUEL K. HOFFMAN. 

